25-Hydroxylation of vitamin D3 by a reconstituted system from rat liver microsomes. |
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| Authors: | Ingemar Björkhem Ronnie Hansson Inger Holmberg Kjell Wikvall |
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| Institution: | 1. Department of Clinical Chemistry, Karolinska Institutet, Stockholm, Sweden;2. Research Centre at Huddinge Hospital, Karolinska Institutet, Stockholm, Sweden;3. Department of Pharmaceutical Biochemistry University of Uppsala, Uppsala, Sweden |
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| Abstract: | Using isotope dilution—mass fragmentography as assay technique, it was shown that highly purified preparations of cytochrome P-450 from rat liver microsomes catalyzed 25-hydroxylation of vitamin D3 when combined with NADPH-cytochrome P-450 reductase and a phospholipid. The rate of conversion was approximately linear with the amount of cytochrome P-450, and was considerably higher than the rate of conversion obtained with crude liver microsomes. The possibility is discussed that the microsomal fraction contains inhibitors of 25-hydroxylase activity, which may be of regulatory importance in vitamin D3 metabolism. |
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